1. Field of the Invention
The present invention relates to an apparatus and a method for simulation of an electromagnetic field which calculates an electric current flowing through each element of an electronic apparatus or an intensity of an electromagnetic field radiated from the electronic apparatus according to analysis in a frequency domain and to a storage medium storing programs used for realization of the simulation apparatus, more particularly relates to an apparatus and a method for simulation enabling execution of simulation processing at a high speed when the electronic apparatus to be analyzed has an angle-modulated wave source and to a storage medium storing programs used for realization of the simulation apparatus.
One of the new regulations being imposed by society on electronic apparatuses is that they must not radiate undesired radio waves and noise of a predetermined level or more. Tough regulations on this have been established in the major countries of the world.
In order to satisfy such radio wave regulations, various countermeasures such as shielding and filtering are used, but to employ these countermeasures, development of the simulation technology enabling quantitative calculation of how much they can attenuate the radio waves is necessary.
In view of this, the present inventors disclosed an invention of simulation technology for calculating the intensity of the electromagnetic field radiated from an electronic apparatus by using the moment method. In order to make this simulation technology practical, it is necessary to develop technology which makes it possible to execute the simulation processing at a high speed.
2. Description of the Related Art
The intensity of the electromagnetic field radiated from the object can be simulated by finding an electric current and a magnetic current flowing through each portion of the object and substituting these in a known theoretical equation of electromagnetic wave radiation. These electric current and magnetic current flowing through each portion of the object can be theoretically acquired by solving Maxwell""s electromagnetic equations under given boundary conditions.
As one solving this, there is the moment method. The moment method is one of the methods of solution of integration equations derived from Maxwell""s electromagnetic equations and is a technique for calculating the electric current and the magnetic current by segmenting an object into small elements. It can handle any three-dimensionally shaped object. As a reference document for this moment method, there is H. N. Wang, J. H. Richmond, and M. C. Gilreath, xe2x80x9cSinusoidal reaction formulation for radiation and scattering from conducting surfacexe2x80x9d, IEEE TRANSACTIONS ANTENNAS PROPAGATION, vol. AP-23, 1975xe2x80x3.
In this moment method, when the configuration of the electronic apparatus to be simulated is segmented into meshes and the frequency to be processed is selected, a mutual impedance, a mutual admittance, and a mutual reaction among meshed elements are found for that frequency by a predetermined calculation, the found mutual impedance etc. and a wave source specified by the configuration information are substituted in simultaneous equations under the moment method, and the equations are solved to find the electric current and the magnetic current flowing through the element.
Namely, when handling a metal object, a method is adopted of segmenting the metal part to be analyzed into meshes, finding a mutual impedance Zij (value at the frequency to be processed) among mesh-like metal elements, and solving the following simultaneous equations under the moment method standing among this mutual impedance Zij, a wave source Vi of the frequency component, and an electric current Ii flowing through the mesh-like metal elements:
[Zij][Ii=[Vi]
where, [] indicates a matrix to find the electric current i and calculating the intensity of the electromagnetic field from a resultant current Ii.
Note that the mutual impedance represents the relationship between an electric field induced by the electric current of one element and the electric current of another element. The mutual admittance becomes necessary when considering the existence of a dielectric and represents the relationship between a magnetic field induced by the magnetic current of one element and the magnetic current of another element. The mutual reaction becomes necessary when considering the existence of a dielectric and represents the relationship between the electric field (magnetic field) induced by the electric current (magnetic current) of one element and the magnetic current (electric current) of another element. Here, the electric current flows through the metal, and both of electric current and magnetic current flow on the surface of the dielectric.
When the intensity of the electromagnetic field radiated from the electronic apparatus is simulated by using this moment method, it is necessary to specify the frequency of the wave source provided by the electronic apparatus and solve the simultaneous equations under the moment method at every specified frequency.
Due to this, up until the present time, when the electronic apparatus is provided with a clock source as the wave source, by applying Fourier transform to the clock signal oscillated by the clock source, the frequency to be analyzed is specified. Further, a method of solving the simultaneous equations under the moment method at every specified frequency to simulate the intensity of the electromagnetic field radiated from the electronic apparatus has been employed.
As one simulating the intensity of the electromagnetic field radiated from the electronic apparatus other than the moment method, there is another simulation technique of analysis in the frequency domain, such as finite element method. In the case where such a simulation technique is used, up to the present time, when the electronic apparatus has a clock source as the wave source, by applying the Fourier transform to the clock signal oscillated by the clock source, the frequency to be analyzed is specified. Further, the method of executing the analysis in the frequency domain at every specified frequency to simulate the intensity of the electromagnetic field radiated from the electronic apparatus has been employed.
Recently, the technique referred to as a spread spectrum clocking (SSC) as shown in FIG. 18A which makes the frequency of the clock source provided by the electronic apparatus swing back and forth by the modulation frequency to attenuate the intensity of the electromagnetic field radiated from the electronic apparatus (technique identical to the technique in which carrier wave fc is angle-modulated with a modulation frequency fm) is now being used.
FIG. 18B is a graph of actually measured data representing an electromagnetic field intensity attenuation effect due to SSC, and FIG. 18C is a graph extracting and enlarging part of the graph of FIG. 18B.
As clear from FIGS. 18B and 18C, by applying the angle modulation to the clock from the clock source, the frequency distribution spreads as shown by F in FIG. 18C, but the intensity of the electromagnetic field thereof becomes E2 and is greatly attenuated compared with the intensity of the electromagnetic field (E1) when the angle modulation is not applied. This will be explained in further detail below by paying attention to one spectrum.
When applying a Fourier transform to the clock signal from a clock source oscillating with a single frequency, as is well known, an oscillating frequency (fc) and higher harmonics (2fc, 3fc, 4fc, . . . ) of the oscillating frequency will appear. However, when applying the Fourier transform to the clock signal from the clock source operating by this spread spectrum clocking, as shown in FIG. 19, an extremely large number of frequencies (side bands) will appear in the vicinity of both the oscillating frequency (fc) and higher harmonics (2fc, 3fc, 4fc, . . . ) thereof in a manner of a shift by each modulation frequency (fm).
Incidentally, the number of these side bands is determined by:
Number of side bands=2xc3x97modulation index+1
Modulation index=(deviation of frequency to be swung by)/fm
Due to this, there was a problem in that, when the intensity of the electromagnetic field radiated from the electronic apparatus provided with the clock source operated by the spread spectrum clocking is simulated, if according to the related art an extremely large number of frequencies must be analyzed, an enormous time is taken for simulating the intensity of the electromagnetic field radiated from the electronic apparatus, and therefore the simulation cannot be carried out in actuality.
The present invention was made in consideration with such a circumstance and has an object thereof to provide a novel simulation apparatus and method enabling execution of the simulation processing at a high speed when the electronic apparatus to be analyzed has the angle-modulated wave source, according to the analysis in the frequency domain, while employing a calculation of the electric current flowing through each element of the electronic apparatus and the intensity of the electromagnetic field radiated from the electronic apparatus and to provide a novel storage medium storing programs used for the realization of the simulation apparatus.
To attain the above object, the apparatus of the present invention comprises a setting unit for selecting a frequency spectrum to be processed from among a plurality of frequency spectrums included in an angle-modulated wave source and setting one or a plurality of sample frequencies from among the spectrums, a calculating unit for calculating an intensity of the electromagnetic field radiated from an electronic apparatus by executing analysis in a frequency domain under a moment method or the like with the sample frequency set by the setting unit as the analyzing frequency, and a computing unit for computing a physical amount to be calculated other than the physical amount calculated by the calculating unit in the frequency domain of the frequency spectrum to be processed, by using a proportional operation, from the physical amount calculated by the calculating unit and the wave source value of the frequency spectrum to be processed. By this, a simulation apparatus enabling high speed simulation of the intensity of the electromagnetic field radiated from the angle-modulated electronic apparatus is provided.